Standard i.e. halogen tubular lighting (“TL”) tubes, as well as typical LED retrofit solutions, provide light in all directions. To create a beam-shape, they are placed in a fixture which comprises a reflector and/or other optical elements to redirect the light from the tube into a desired beam shape.
LED technology allows for the integration of the light generation elements (the LEDs) and the beam shaping optics into the tubular lighting housing, thereby eliminating the need for expensive external housings and optics. Current tubular LED (known as “TLED”) solutions are known which integrate optics into the tubular housing to optimize efficiency and to create a desired beam shape. For example, lenses or total internal reflection collimators may be mounted over on the LEDs in the tubular housing.
Although this does allow for the creation of a beam shape, this also lead to a very spotty appearance of the tube (due to the close proximity of the optics and the LEDs), which in some situations is disliked for aesthetic reasons, and may even be uncomfortable due to the high peak brightness.
Another disadvantage of typical lenses used for beam shaping is that for white light lighting devices they generally cause color differences as a function of angle of the exiting light. This is caused by color non-uniformities of the exit window of a typical white LED, which are typically based on the use of blue emitting LED die covered by a phosphor which partially converts this blue light into larger wavelengths (e.g. yellow), to form white light (based on the combination of the original blue light and the phosphor-converted yellow light). Typically, this means a more bluish light from the center of the LED, while more yellowish light is emitted from the edges of the LED.
Typically, when beam shaping this light with lenses or collimators, these spatial color differences are converted to angular color differences causing the center of the beam to be bluish and the edges yellowish (or vice versa, depending on the type of optics used). In certain applications this is highly disliked, especially in applications where the light is used to illuminate white objects.